Standardized accessory mounting rails are well known for use with firearms. Most common is the Picatinny, Weaver, or MIL-STD 1913 rail, referred to herein collectively or interchangeably as a “Picatinny” rail or mounting rail. A Picatinny rail can range in length from less than one inch, such as for mounting a light or laser indicator to the underside of a pistol frame or for mounting a single scope ring, to the full length of a rifle. Typically, these standardized accessory attachment rails are formed or secured along the length of the frame, stock, or barrel parallel to the bore of the firearm barrel so that any sighting device, scope, or light is substantially aligned with the barrel either at the top, bottom, or side of the firearm.
In some cases, “open” or “iron” sights (sights that do not include any lens or projected beam of light) must be removed or rendered unusable in order to mount an accessory rail. In other cases, the firearm (such as a bolt action rifle) may not have any open sights and sighting is dependent on use of a rail-mounted telescopic or holographic sighting system or the addition of upstanding (or flip-up) iron sight elements. For some users, the consequences of a scope or lighted sight system failure are too great not to have some kind of pre-aligned back up iron sights (BUIS) in place in addition to whatever optics are mounted on the accessory rail.
Separate front and/or rear (fixed or flip-up) iron sights can be rail mounted along with a scope or holographic sight in some cases. These, however, add complexity, cost, weight and bulk to the weapon system. Some of these shortcomings are discussed in U.S. Patent Application Publication No. 2008/0092423 by Keng.
As another example, a shotgun may be used for hunting with a rail-mounted scope, but may also be used for home defense where a magnifying scope is undesired. Removal of the scope leaves it without any sights unless separate iron sights are installed in its place. Shotguns are also used in military and civilian law enforcement tactics where a need for back up iron sights along with a rail mounted optical sight is present. This need is discussed in U.S. Patent Application Publication No. 2003/0140546 by Kay. In Kay, an elevated rear sight element is integrated with a Picatinny mounting rail. This system raises the sight line a significant distance above the bore axis and requires the addition of a separate, M16-style elevated front sight to the forward end of the barrel.
Consideration of the Keng and Kay Patent Application Publications will provide context for and reveal the significance of the present invention.